Remove unused columns in word and search_name tables

Removes a few unused columns to further reduce memory footprint.

word:
 - removed `location` and `word_trigram` (hopefully also solves the issues with postgres 2.0)

search_name_* (with the exception of search_name itself):
 - removed `name_address_vector`, `importance`, `country_code`
 - save full geometry in centroid column (solves [trac ticket 4719](https://trac.openstreetmap.org/ticket/4719), couldn't see any degradation in indexing performance on planet import)

Updating existing databases should be straightforward.